Investigating the effect of direction on the limits of haptic retargeting

Haptic Retargeting enables spatially decoupled physical objects to provide haptic feedback for multiple virtual objects in Virtual Reality (VR). By decoupling the virtual hand from its real position, through Hand Redirection, multiple virtual objects can be mapped to a single physical proxy. However, redirection beyond a detectable level is disruptive to the user experience. The limits of haptic retargeting have mainly been explored in one primary direction-the user reaching forwards. We designed an experiment with participants performing reaching movements across 8 reaching directions in the horizontal plane, with a hand redirection of up to 30°. We identify an overall haptic retargeting limit and find that a physical proxy can be remapped to virtual objects of up to 16.14° away. We find a significant effect of reaching direction on the limit. In practice, however, these differences are small, measuring only a couple of degrees, translating to approximately 1cm across a 30cm reach. We argue that, while the psychology literature might suggest the need for specific directional limits and while we do find an effect of direction on retargeting limits, interaction designers can mitigate these requirements by applying slightly conservative global retargeting limits. Our contributions further the community's knowledge of both how to deploy haptic retargeting in interaction without compromising the user's experience and how visual and proprioceptive cues interact in peripersonal space in VR.